An optical waveguide or fiber may be drawn from a consolidated glass preform; the glass preform being typically formed by sintering a soot preform. Soot preforms may be formed by suitable methods such as, for example, chemical vapor deposition (CVD). Various dopants may be added to alter the optical properties or other characteristics of the optical waveguide or glass or soot preform. For example, certain halogen-containing compounds may be used as dopants to dope the soot preform during a consolidation process. In one example, a soot preform may be doped with chlorine to modify the viscosity of glass formed from the soot preform. As a further example, a soot preform may be doped with fluorine to reduce the refractive index of a waveguide formed from the soot preform as compared to undoped silica. However, for some applications it is desirable to provide higher levels of doping than may be possible or cost-effectively achieved with known doping methods. Moreover, known processes may create undesirably large amounts of waste gases and may require substantial amounts of costly gases. Similarly, it may be desirable to provide more efficient drying of soot preforms and a reduction in waste gases produced during such drying processes.